ROSAT has discovered a new group of isolated neutron stars characterized by soft black-body like spectra ( kT \sim 50-120 eV ) , apparent absence of radio emission and no association with supernovae remnants .
So far only six such sources are known .
A small fraction of these stars exhibit X-ray pulsations with relatively long periods of the order of 10 sec .
Two very different mechanisms may be envisaged to explain their properties .
The neutron stars may be old and re-heated by accretion from the ISM in which case their population properties could provide information on past stellar formation and secular magnetic field decay .
Alternatively , this group may at least partly be made of relatively young cooling neutron stars possibly descendant from magnetars .
We review the last observational results and show how they can shed light on the evolutionary path of these new objects within the whole class of isolated neutron stars .

KEYWORDS : neutron stars ; pulsars ; magnetars